Electrostatic printing



United States Patent f 3,308,731 ELECTROSTATIC PRINTING Roger GeorgeOlden, Princeton, N.J., assignor to Radio Corporation of America, acorporation of Delaware Original application Mar. 22, 1961, Ser. No.97,611, now Patent No. 3,210,185. Divided and this application Jan. 7,1965, Ser. No. 424,101 1 Claim. (Cl. 951.7)

This is a division of application Ser. No. 97,611, filed Mar. 22, 1961,and issued as US. Patent No. 3,210,185 on Simultaneous IdenticalElectrostatic Image Recording on Multiple Recording Elements.

This invention relates generally to electrostatic printing, and moreparticularly to novel apparatus for exposing a plurality ofelectrophotographic recording elements simultaneously. The novelapparatus of the present invention is particularly useful for makingduplicate copies of an image by electrophotographic means.

Previously, duplicate electrostatic prints have been made by exposing aplurality of uniformly charged, electrophotographic recording elementsto the same light image successively and developing each recordingelement separately. Data read-out time in electronic computers, forexample, is at a premium. Therefore, successive read-out for makingduplicate copies of computer data is not desirable. Heretofore, ifduplicate electrostatic prints were desired in a period of time lessthan that required to produce these prints successively in one automaticprocessing machine, duplicate machines had to be employed. Sincemachines for automatically producing electrostatic prints are expensive,the use of duplicate apparatus to speed production may be prohibitive inmany instances. Accordingly, it is an object of the present invention toprovide improved means for producing electrostatic prints faster andmore economically than is possible by prior art methods and apparatus.

Another object of the present invention is to provide improved automaticapparatus for making a plurality of electrostatic prints insubstantially the same amount of time required to process a singleelectrostatic print. Still another object of the present invention is toprovide improved apparatus for making a plurality of electrostaticprints by employing novel means to expose a plurality of uniformlycharged electrophotographic recording elements simultaneously.

A further object of the present invention is to provide improved meansfor making simultaneously a plurality of electrostatic prints, includinga master print useful in making reproduction by another reproductiveprocess.

Briefly, a preferredembodiment of the improved apparatus of the presentinvention comprises automatic means for processing a plurality ofrecording elements simultaneously. In each of the embodiments of theapparatus described herein, a plurality of recording elements areexposed simultaneously. In one embodiment of the present invention, allof the recording elements are oriented similarly so that the backingsheet of one recording element is in contact with the photoconductivelayer of an adjacent recording element during the exposure step in theprocess. In another embodiment of the present invention, two recordingelements are arranged so that their photoconductive layers contact eachother during the exposure step, there-by providing for a mirror-imagemaster print that may be used in other reproductive processes.

Other novel features of the present invention, both as to itsorganization and methods of operation, as well as additional objects andadvantages thereof, will be described in greater detail by reference tothe accompanying drawings, in which similar reference charactersdesignate similar parts throughout, and in which:

FIGS. 1A, 1B, and 1C show three electrophotographic ice Patented Mar.14, 1967 recording elements undergoing successive steps of charging,exposing, and developing, respectively, in the process of electrostaticprinting, in accordance with the present invention;

FIG. 2 is a schematic diagram of one embodiment of improved apparatus,employing a thin-window cathode ray tube, for exposing a plurality ofelectrophotographic recording elements simultaneously in the process ofmaking duplicate electrostatic prints, in accordance with the presentinvention;

FIG. 3 is a schematic diagram of another embodiment of improvedapparatus, employing light means, for exposing a plurality ofelectrophotographic recording elements simultaneously, in accordancewith the present invention; and

FIG. 4 is a schema-tic diagram of still another embodiment of improvedapparatus, employing a thin-window cathode ray tube, for exposing aplurality of electrophotographic recording elements simultaneously in amanner to produce one master copy for use in another reproductiveprocess, in accordance with the present invention.

Referring now to FIGS. 1A, 1B, and 1C, there are shown threeelectrophotographic recording elements 10, 12, and 14 in some of thesteps of the process of electrophotographic printing, in accordance withthe present invention. The recording elements 10, 12, and 14 comprisebacking sheets 10a, 12a, and 14a having photoconductive layers 1%, 12b,and 14b on their upper surfaces, respectively. The backing sheets 10a,12a, and 14a may comprise any suitable translucent material, such aspaper and the like, and the photoconductive layers 10b, 12b, and 1412may comprise photoconductive zinc oxide embedded in a. resin binder. Thephotoconductive layers 10b, 12b, and 14b may also contain differentamounts of dyes mixed r in the binder for the purpose of rendering eachsuccessive layer more sensitive to electromagnetic radiation, for thepurpose hereinafter appearing.

Referring now to FIG. 1A, the recording elements 10, 12, and 14 areshown in the process of receiving a uniform electrostatic charge. Therecording elements 10, 12, and 14 are placed on a sheet 16 ofelectrically conducting material so that their respective backing sheets10a, 12a, and 14a are in contact with the sheet 16. The sheet 16 isgrounded. A corona discharge device, that is, a charging unit 18 isconnected to a source (not shown) of relatively high unidirectionalvoltage (about 6,000 volts) for producing a corona discharge from wires20 of the charging unit. The charging unit 18 is moved over thephotoconductive layers 10b, 12b, and 14b of recording elements so as todeposit a uniform negative electrostatic charge on the photoconductivelayers.

In the next step, the uniformly charged recording elements 10, 12, and14 are arranged one behind the other, front to back, so that the backingsheet of one recording element is in contact with the photoconductivelayer of an adjacent recording element, as shown in FIG. 1B. When soarranged, the recording elements 10, 12, and 14 are exposedsimultaneously by an image of electromagnetic radiation directed ontoone recording element, the recording element 10, for example, with anintensity sufficient to penetrate this and other translucent recordingelements and to permit a latent electrostatic image to be formed on eachof the photoconductive layers 10b, 12b, and 14b of the recordingelements. The image of elec tromagnetic radiation is directed preferablyperpendicularly to the photoconductive layers, as illustrated by thearrows 22 in FIG. 1B. The image of electromagnetic radiation may beformed with visible light, infra red radiation, and X-rays, for example.The recording element that is farthest from the source ofelectromagnetic radiation need not be transparent because itsphotoconductive layer can be exposed through the translucent elements infront of it. If, for example, the photoconductive layers 1%, 12b, and14b were sensitized with fluorescein, rose bengal and methylene blue,respectively, each of the stacked recording elements 10, 12, and 14would be sensitive to electromagnetic radiations in a different spectralrange. Thus, differently sensitized recording elements may be exposedsimultaneously by a colored image, in cluding light in all the spectralranges, to produce separation prints useful in some color printingmethods.

After the simultaneous exposure of the recording elements 10, 12, and14, they are separated from each other and developed separately, asshown in FIG. 1C. To this end, each of the recording elements 10, 12,and 14 is brushed with a developing mixture 24 of tribe-electricallycharged particles, comprising, for example, a powdered dye materialmixed with iron filings. The developing mixture 24 is applied to thelatent images by means of a magnet 26, as described, for example, inU.S. Patent 2,874,063 to H. G. Greig.

Referring now to FIG. 2, there is shown schematically apparatus 30 formaking two electrostatic prints simultaneously. One web of a continuousrecording element 32, stored on a roll 34, is pulled past the window 35of a thin-window cathode ray tube 37 by means of a pair of drive rollers36 and 38, and guide rollers 39 and 40. The drive rollers 36 and 38 aredriven by any suitable means (not shown). Another web of a continuousrecording element 42, stored on a roll 44, is pulled over the recordingelement 32 at the site where the recording element 32 comes in contactwith the window 35, by means of a pair of drive rollers 46 and 48, andguide rollers 49 and 50. The recording element 42 is directly behind,and in contact with, the recording element 32 at the window 35, theexposure station. The drive rollers 46 and 48 are driven by any suitablemeans (not shown). The recording elements 32 and 42 are similar to therecording elements 10, 12, and 14, previously described, and they havephotoconductive layers 32a and 42a, respectively, on the sides that facethe window 35 of the tube 37.

The recording element 32 is pulled past a developer trough 52 and afuser 54 by means of a pair of drive rollers 56 and 58, and a guideroller 60. The developer trough 52, as well as other developer apparatusdescribed herein, may comprise the apparatus described by A. Stavrakiset 'al. in U.S. Patent No. 2,910,964. The recording element 42 is pulledpast a developer trough 62 and a fuser 64 by means of a pair of driverollers 66 and 68. A charging unit 70, with voltage applied to itselements as indicated, is disposed about the webs of the recordingelements 32 and 42 to charge the photoconductive layers 32a and 42anegatively, in a manner well known in the art. The charging unit 70 islocated between the guide rollers 39 and 40 and between the guiderollers 49 and 50.

The thin-window cathode ray tube 37 comprises means to write on aphosphor screen with an electron beam in accordance with the principleswell known in the television art, as described, for example, in RCAReview, September 1957, vol. XVIII, No. 3, at pages 343 to 350. Theelectronic circuitry for operating the tube 37 is not shown because itforms no part of the instant invention. The cathode ray tube 37 isformed with a relatively thin window 35 which is elongated in onedirection (perpendicular to the direction of travel of the recordingelements). It will be understood that when the phosphor screen (notshown) on the window 35 is caused to luminesce by an electron beamimpinging on it, the image of the light from the phosphor screen willexpose the recording elements 32 and 42. In order to prevent excessivewear of the window 35 due to friction, a web 72 of transparent plasticmaterial, such as a clear, tough plastic material sold under thetrademark Mylar, is caused to move between the window 35 and therecording element 32.

To this end, the web 72, stored on a roll 74, is pulled over the window35 by a takeup roller 76, by any suitable means known in the art. Inpractice, the web 72 is pulled over the window 35 at a relatively muchslower rate than the recording elements 32 and 42.

The operation of the apparatus 30, in accordance with the presentinvention, will now be described. The photoconductive layers 32a and 42aof the recording elements 32 and 42 are charged negatively by thecharging unit 70 and moved into contact with each other and with the web72 over the window 35 of the tube 37. When in contact with each other,the recording elements 32 and 42 are exposed simultaneously by lightfrom the fluorescent Window 35. The light is of suflicient intensity toexpose the photoconductive layers 32a and 42a of both of the recordingelements 32 and 42. After exposure, the recording elements 32 and 42move through the developer troughs 52 and 62 where they are developed.From the developer troughs 52 and 62, the recording elements 32 and 42pass through the fusers 54 and 64 where the developer mixture is fusedonto the recording elements, and the electrostatic print is finished.

Referring now to FIG. 3, there is shown apparatus for exposing aplurality of recording elements simultaneously to visible light in theprocess of electrostatic printing according to the present invention. Arecording ele ment 81, wound on a roll 82, is pulled past a groundedplaten 83, a developer trough 84, and a fuser by means of drive rollers86 and 87, and guide rollers 88, 89, and 90. The drive rollers 86 and 87are driven by any suitable means, such as an electric motor (not shown).A continuous recording element 91, stored on a roll 92, is pulled overthe recording element 81 at the site of the platen 83, through adeveloper trough 94, and a fuser by means of drive rollers 96 and 97 andguide rollers 98 and 99. The drive rollers 96 and 97 are driven by anysuitable means (not shown). A pair of corona discharge units 100, 102are disposed to charge the photoconductive lay ers 81a and 91a of therecording elements 81 and 91, respectively, with a uniform negativecharge. The photoconductive layers 81a and 91a are separated from eachother by the backing sheet of the recording element 91, and the backingsheet of the recording element 81 is in contact with the grounded platen83.

Means are provided to expose the recording elements 81 and 91simultaneously. To this end, electromagnetic radiation, such as lightfrom a light source 104, is directed onto the platen 83, the exposurestation, by means of an optical projector 106. A transparency 108, suchas a photographic negative, for example, disposed between the lightsource 104 and the projector 106, produces a light image on thephotoconductive surface 91a of recording element 91. In accordance withthe present invention, the light image is of suflicient intensity topenetrate the translucent recording element 91 and to expose the photoconductive layer 81a of the recording element 81. After the simultaneousexposure of the recording elements 81. and 91, the recording elementsare developed .and fused in the manner described for the apparatus 30 ofFIG. 2.

Referring now to FIG. 4, there is shown apparatus for exposing tworecording elements simultaneously in a manner to produce a normalelectrostatic print and a master print from which other prints may bemade. A recording element 112, stored on a roll 113, is pulled acrossthe window 35 of the thin-window cathode ray tube 37 and thensuccessively through a first developer trough 114, a second developertrough 115, and a fuser 116 by means of suitably driven drive rollers117 and 11 8, and guide rollers 119, 120, '121, and 122. A recordingelement 123, stored on a roll 124, is pulled over the recording element112 at the window 35 of the tube 37, and then successively through adeveloper trough 125, and a fuser 126 by means of suitably driven driverollers 127 and 128, and guide rollers 129, 130, 131, 132, and 133. Acorona discharge unit is disposed about the recording elements 112 and123 in a manner to charge adjacent photoconductive layers 112w and 123a,respectively, with a negative charge. It will be noted that in theembodiment of the apparatus shown in FIG. 4, the photoconductive layers112a and 123a of the recording elements 112 and 123, respectively, areadjacent to each other, face to face.

In operation, the uniformly charged recording elements 112 and 123 areexposed simultaneously by means of writing on the phosphor screen (notshown )on the window 35, as explained heretofore for the apparatus 30 ofFIG. 2. After exposure, the recording elements are separated. Therecording element 123 is developed in the developer trough 125, and thedeveloped image is fused in the fuser 126.

Since the recording element 112 was exposed with radiant energy thatfirst had to penetrate the backing sheet of the recording element 112,the latent image produced on the photoconductive layer 112a of therecording element 112 is a mirror image of the true image. This mirrorimage is developed in the developer tank 114. By means of a pair ofopposed pressure rollers 136 and 138, a uniformly, negatively chargedWeb of uncoated paper 140 can be pressed against the developed image onthe photoconductive layer 112a of the recording element 112 to cause theunfused developed image on the recording element 112 to be transferredto the paper 140.

The web of paper 140, stored on a roll 142, is pulled past a chargingunit 144, between the rollers 136 and 138, and through a fuser 146 bymeans of suitably driven drive rollers 148 and 150, and a guide roller152. Thus, the unfused powdered image transferred to the charged paper140 can be fused in the fuser 146. After the transfer process, therecording element 112 may be developed once more in the developer tank115 and fused in the fuser 116. The developed image appearing upon therecording element 112 is a mirror image of the images appearing on therecording element 123 and on the paper 140*. Because the image on therecording element 112 is a mirror image, the developed recording element112 can be used in other recording processes, such as by transfer to amultilith master for the multilith process of reproduction.

From the foregoing description, it will be apparent that there has beenprovided improved means for making duplicate electrostatic prints. Bymeans of the apparatus shown and described, a plurality of recordingelements, superimposed on each other at an exposure station, are exposedsimultaneously with electromagnetic radiation of sufficient intensity topenetrate all of the recording elements. While the apparatus has beenillustrated in schematic form, variations in the apparatus coming withinthe spirit of this invention will, no doubt, readily suggest themselvesto those skilled in the art. For example, a greater number of recordingelements may be exposed simultaneously than the number described andillustrated. Hence, it is desired that the foregoing description shallbe considered merely as illustrative and not in a limiting sense.

What is claimed is:

Apparatus for processing two electrophotographic recording elementssimultaneously to provide an original copy and a mirror-imaged mastercopy of an image, said master copy comprising means from whichadditional copies of said image may subsequently be made, each of saidelements comprising a backing sheet and a photoconductive layer thereon,said apparatus comprising means to charge each of said elementselectrostatically, an exposure station, means to guide said elementsthrough said charging means to said exposure station so that saidphotoconductive layers of said two elements are in contact with eachother at said exposure station, means to direct an image ofelectromagnetic radiation through said elements to expose saidphotoconductive layers simultaneously and to produce electrostaticimages thereon, the layer of one said elements being exposed through itsbacking whereby the electrostatic image produced on said one element isthe mirror image of that produced on the other of said elements, firstmeans to develop said electrostatic image on said one element, means toguide said one element through said first means to develop saidelectrostatic image thereon; sheet material, means to press said sheetmaterial against said developed image on said one element to transfer atleast part of said developed image from said one element to said sheetmaterial to produce a mirror image of said developed image on said sheetmaterial, second means to redevelop said one element to restore saiddeveloped image thereon, means to guide said one element through saidsecond means to redevelop and to restore said developed image whereby toprovide said master copy from which other copies may subsequently bemade, third means to develop said other of said elements, and means toguide said other of said elements through said third means to developthe electrostatic image thereon whereby to provide said original copy.

References Cited by the Examiner UNITED STATES PATENTS 2,182,142 12/1939Ball l2.20 2,749,792 6/1956 Kelly 95-l2.20 2,952,796 9/1960 Crews 954.5X 2,962,374 11/1960 Dessauer 95--1.7 X 3,057,275 10/1962 Walkup 95- 173,145,632 8/1964 McNaney 95-1.7

JOHN M. HORAN, Primary Examiner.

